The invention relates to blind rivets and blind rivet type fastening devices which may be used for blind riveting various attachments to workpieces for instance of sheet metal.
Swiss Pat. No. 501846 discloses blind rivets which consist of a single piece of the same material. It specifies as manufacturing materials aluminum, copper, mild steel and also synthetic material. Proper functioning of this type of rivet, however, cannot be warranted, particularly if it is made of synthetic material because it would not stand the required deformation for the setting of the rivet. If a hard synthetic material is used for making the blind rivet, it would break during setting, and if a soft synthetic material is used, the blind rivet would after setting revert to its original shape due to the elasticity of the synthetic material.
Other heretofore known blind rivets according to Austrian Pat. 222436 consist of two parts. They comprise a hollow rivet of relatively soft material as for instance mild steel and are provided with a manufactured head. Non-separably connected with the hollow rivet is a setting mandrel of hard material, for instance tool steel. The mandrel has a draw shank which projects from the head end of the hollow rivet to provide for clamping it into a rivet setting device of well-known type. At its other end the setting mandrel has an enlarged head which is larger than the cylindrical or conical through bore of the hollow rivet. Behind the enlarged head and progressively in the direction of the draw shank, the mandrel is provided with a rib, a milled shaft section, another rib, a break off connection and finally with an upsetting cone. These individual mandrel portions all have different diameters which are larger than the draw shank diameter. During the setting of the blind rivet the through bore of the hollow rivet is plastically enlarged or deformed by the upsetting and enlarging cones, respectively, and the enlarged mandrel head together with the hollow rivet form a closure head or cap. After the closure head or cap has been formed the draw shank separates from the mandrel at the break-off connection.
Blind rivets of this type are unsuitable for use in various kinds of attachment fastening devices. Moreover, these prior art blind rivets are not detachable. The hollow rivet and the setting mandrel must be manufactured separately and then assembled into a blind rivet. This makes conventional blind rivets definitely expensive.
West German petty Pat. No. 1,993,274 discloses a mounting body with a spreading device of synthetic material, in which the spreading bolt is retained by a sprayed on film in order to avoid tipping during the insertion impact.